Cu@Au(Ag)/Pt nanocomposite as peroxidase mimic and application of Cu@Au/Pt in colorimetric detection of glucose and l-cysteine

Nanomaterial-based artificial peroxidase has attracted extensive interests due to their distinct advantages over natural counterpart. Cu@Au/Pt and Cu@Ag/Pt nanocomposite with rambutan-like structure were prepared and discovered to function like peroxidase, which was illustrated by catalyzing the oxidation reaction of 3,3′,5,5′-tetramethylbenzidine (TMB) accompanied with a blue color change. Steady-state investigation indicates that the catalytic kinetics of Cu@Au/Pt and Cu@Ag/Pt all followed typical Michaelis–Menten behaviors and Cu@Au/Pt showed a strong affinity for H₂O₂, while Cu@Ag/Pt showed strong affinity for TMB. The color change and absorbance intensity strongly depend on the concentration of H₂O₂, thus the direct determination of H₂O₂ and indirect detection of glucose were demonstrated using Cu@Au/Pt with a detection limit of 1.5 μM and 6 μM, respectively. What is more important, the method was applied for detection of glucose in 50% fetal bovine serum with a detection limit of 80 μM, which is much lower than the lowest glucose content in blood for diabetes (7 mM). Moreover, the Cu@Au/Pt nanocomposite were also successfully applied for sensing l-cysteine because of the inhibition effect. Considering the good peroxidase-like activity and novel structure, Cu@Au(Ag)/Pt is expected to have a wide range of applications in bioassays and biocatalysis.

Cu@Au(Ag)/Pt nanocomposite possess good peroxidase-like activity and can be used for detection of glucose and l-cysteine.     

Colorimetric sensing of glucose and GSH using core–shell Cu/Au nanoparticles with peroxidase mimicking activity

The catalytic properties of bimetallic nanoparticles have been widely studied by researchers in many fields. In this paper, core–shell Cu/Au nanoparticles (Cu/Au NPs) were synthesized by a simple and mild one-pot method, and their peroxidase activity was proved by catalyzing the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) with color change to blue. The change of solution color and absorbance strongly depends on the concentration of H₂O₂, so it can be used for direct detection of H₂O₂ and indirect detection of glucose. What''s more, GSH can efficiently react with the hydroxyl radicals from H₂O₂ catalyzed by core–shell Cu/Au NPs to inhibit the production of ox-TMB. Thus, the concentration of GSH can be determined by the decrease in the absorbance of the solution at 652 nm. The results showed that our proposed strategy had good detection range and detection limit for the detection of glucose and GSH. This method has been used in the detection of practical samples and has great application potential in environmental monitoring and clinical diagnosis.

Core–shell Cu/Au nanoparticles were synthesized by a one pot method, their peroxidase activity was proved by catalysing the oxidation of 3,3′,5,5′-tetramethylbenzidine with colour change to blue. Results showed a good range and limit for the detection of glucose and GSH.     

Mixed-solvent liquid exfoliated MoS2 NPs as peroxidase mimetics for colorimetric detection of H2O2 and glucose

Ultra-small molybdenum disulfide nanoparticles (MoS₂ NPs) were prepared by a facile liquid exfoliation method with ethanol/water as the solvent. The produced MoS₂ NPs were of high purity due to the easily removable ethanol/water solution. The prepared MoS₂ NPs exhibited an intrinsic peroxidase-like activity in analogy to that of horseradish peroxidase (HRP). A custom-made spectrometer was employed to investigate the peroxidase-like activity of MoS₂ NPs in the presence of H₂O₂ and glucose. The change in absorption detected from MoS₂ NPs is proportional to the amount of target. The calibration curve of H₂O₂ and glucose shows a good relationship between the concentration of target and the change in the absorption of MoS₂ NPs. The limit of detection of H₂O₂ and glucose achieved by this method could approach 1.25 μM and 7 μM respectively. This method has been applied for the detection of glucose in serum from humans. Therefore, these produced MoS₂ NPs offer an alternative high-efficiency and economic way to detect diabetes.

Ultra-small molybdenum disulfide nanoparticles (MoS₂ NPs) prepared by a facile liquid exfoliation method is capable of detecting the presence of H₂O₂ and glucose. This novel colorimetric method offers an alternative way to detect diabetes.     

Convenient and sensitive colorimetric detection of melamine in dairy products based on Cu(ii)-H2O2-3,3′,5,5′-tetramethylbenzidine system

The illegal adulteration of melamine in dairy products for false protein content increase is a strong hazard to human health. Herein, a simple and sensitive colorimetric method was developed for the quantification of melamine in dairy products based on a Cu²⁺-hydrogen peroxide (H₂O₂)-3,3′,5,5′-tetramethylbenzidine (TMB) system. In this strategy, Cu²⁺ exhibits peroxidase-like activity and can catalyze the oxidation of TMB to oxidized TMB (oxTMB) in the presence of H₂O₂ with a blue colour change of the solution. However, the presence of melamine quickly interacts with H₂O₂ leading to the consumption of H₂O₂ and thus strongly hinders the oxidation of TMB. Under the optimal conditions, the absorbance change of oxTMB has a linear response to the concentration of melamine from 1 to 100 μM with a detection limit of 0.5 μM for melamine. The proposed method has many merits including more simplicity, good selectivity, and more cost-effectiveness without using any nanomaterials. The method was further successfully applied to detect melamine in dairy products including milk and infant formula powder.

Convenient and sensitive colorimetric detection of melamine in dairy products based on a Cu(ii)-H₂O₂-3,3′,5,5′-tetramethylbenzidine system was reported.     

Mesoporous MnFe2O4 magnetic nanoparticles as a peroxidase mimic for the colorimetric detection of urine glucose

Mesoporous MnFe₂O₄ magnetic nanoparticles (mMnFe₂O₄ MNPs) were prepared with a one-step synthesis method and characterized to possess intrinsic peroxidase-like activity, and had obvious advantages over other peroxidase nanozymes in terms of high catalytic affinity, high stability, mono-dispersion, easy preparation, and quick separation. The mMnFe₂O₄ MNPs were used as a colorimetric sensor for indirect sensing of urine glucose based on the sensing principle that H₂O₂ can be produced from glucose oxidation catalyzed by glucose oxidase (GOx), and under the catalysis of the mMnFe₂O₄ MNPs nanozyme, H₂O₂ can oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) to produce a blue color in a few minutes. This sensor is simple, cheap, sensitive, and specific to glucose detection with a detection limit of 0.7 μM, suggesting its potential for on-site glucose detection.

Schematic illustration of glucose detection with glucose oxidase (GOx) and mMnFe₂O₄ MNPs-catalyzed system.     

Molecular imprinting on PtPd nanoflowers for selective recognition and determination of hydrogen peroxide and glucose

PtPd nanoflowers (PtPd NFs) exhibit intrinsic peroxidase-like activity as nanozymes, but the nanozymes lack substrate specificity and have low catalytic activity. Herein, a molecularly imprinted nanogel on PtPd NFs was prepared by using 3,3′,5,5′-tetramethylbenzidine (TMB) as the template through the aqueous precipitation polymerization method. After the TMB was washed out, many substrate binding pockets were retained in the PtPd NFs. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and powder X-ray diffraction (XRD) were employed to characterize the molecularly imprinted polymer (MIP) PtPd nanoflowers (T-MIP-PtPd NFs). The obtained T-MIP-PtPd NFs exhibited enhanced catalytic activity and specific recognition for TMB. Compared with PtPd NFs, T-MIP-PtPd NFs showed a linear range from 0.01–5000 μM and a detection limit of 0.005 μM toward the detection of H₂O₂. Glucose can also be sensitively detected through cascade reaction by the T-MIP-PtPd NFs and glucose oxidase. Therefore, molecular imprinting on nanozymes technology shows promising application in biocatalysis and sensing fields.

PtPd nanoflowers (PtPd NFs) exhibit intrinsic peroxidase-like activity as nanozymes, but the nanozymes lack substrate specificity and have low catalytic activity.     

Sweetsop-like α-Fe2O3@CoNi catalyst with superior peroxidase-like activity for sensitive and selective detection of hydroquinone

Hydroquinone (HQ) is poorly degradable in the ecological environment and is highly toxic to human health even at a low concentration. The colorimetric method has the advantages of low cost and fast analysis, which provides the possibility for simple and rapid detection of HQ. In this work, a new colorimetric method has been developed for HQ detection based on a peroxidase-like catalyst, α-Fe₂O₃@CoNi. This sweetsop-like α-Fe₂O₃@CoNi catalyst enables H₂O₂ to produce hydroxyl (˙OH), leading to the oxidization of colorless 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxTMB. In the presence of HQ, the blue oxTMB is reduced to colorless, which allows for colorimetric detection of HQ in water samples. This method has been validated by detecting HQ in water samples with high selectivity, rapid response, broad detection range (0.50 to 30 μM), and low detection limit (0.16 μM).

A sweetsop-like α-Fe₂O₃@CoNi catalyst with superior peroxidase-like activity was synthesized and successfully applied to the detection of hydroquinone (HQ) based on the colorimetric principle.     

A nano-sized Cu-MOF with high peroxidase-like activity and its potential application in colorimetric detection of H2O2 and glucose

Peroxidase widely exists in nature and can be applied for the diagnosis and detection of H₂O₂, glucose, ascorbic acid and other aspects. However, the natural peroxidase has low stability and its catalytic efficiency is easily affected by external conditions. In this work, a copper-based metal–organic framework (Cu-MOF) was prepared by hydrothermal method, and characterized by means of XRD, SEM, FT-IR and EDS. The synthesized Cu-MOF material showed high peroxidase-like activity and could be utilized to catalyze the oxidation of o-phenylenediamine (OPDA) and 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H₂O₂. The steady-state kinetics experiments of the oxidation of OPDA and TMB catalyzed by Cu-MOF were performed, and the kinetic parameters were obtained by linear least-squares fitting to Lineweaver–Burk plot. The results indicated that the affinity of Cu-MOF towards TMB and OPDA was close to that of the natural horseradish peroxidase (HRP). The as-prepared Cu-MOF can be applied for colorimetric detection of H₂O₂ and glucose with wide linear ranges of 5 to 300 μM and 50 to 500 μM for H₂O₂ and glucose, respectively. Furthermore, the specificity of detection of glucose was compared with other sugar species interference such as sucrose, lactose and maltose. In addition, the detection of ascorbic acid and sodium thiosulfate was also performed upon the inhibition of TMB oxidation. Based on the high catalytic activity, affinity and wide linear range, the as-prepared Cu-MOF may be used for artificial enzyme mimics in the fields of catalysis, biosensors, medicines and food industry.

A Cu-MOF with high peroxidase-like activity was prepared and could be used for colorimetric detection of H₂O₂ and glucose with high selectivity and good linear range (50–500 μM).     

A cobalt-doped iron oxide nanozyme as a highly active peroxidase for renal tumor catalytic therapy

The Fe₃O₄ nanozyme, the first reported nanozyme with intrinsic peroxidase-like activity, has been successfully employed for various diagnostic applications. However, only a few studies have been reported on the therapeutic applications of the Fe₃O₄ nanozyme partly due to its low affinity to the substrate H₂O₂. Herein, we report a new strategy for improving the peroxidase-like activity and affinity of the Fe₃O₄ nanozyme to H₂O₂ to generate reactive oxygen species (ROS) for kidney tumor catalytic therapy. We showed that cobalt-doped Fe₃O₄ (Co@Fe₃O₄) nanozymes possessed stronger peroxidase activity and a 100-fold higher affinity to H₂O₂ than the Fe₃O₄ nanozymes. The lysosome localization properties of Co@Fe₃O₄ enable Co@Fe₃O₄ to catalyze the decomposition of H₂O₂ at ultralow doses for the generation of ROS bursts to effectively kill human renal tumor cells both in vitro and in vivo. Moreover, our study provides the first evidence that the Co@Fe₃O₄ nanozyme is a powerful nanozyme for the generation of ROS bursts upon the addition of H₂O₂ at ultralow doses, presenting a potential novel avenue for tumor nanozyme catalytic therapy.

Cobalt dopant in Fe₃O₄ nanozymes improved their binding affinity to H₂O₂ and enhanced the tumor catalytic therapy efficacy.     

Fluorescence quenching mediated detection of hydrogen peroxide using tungsten incorporated graphitic carbon nitride nanoflakes

A reliable, non-enzymatic detection for H₂O₂ with high sensitivity and accuracy is of profound importance and getting considerable interest due to its usefulness in biological systems. Therefore, this work was aimed to develop a sensitive method for the detection of H₂O₂ using rhodamine B as a fluorescence system and tungsten doped graphitic carbon nitride (W/GCN) as catalysts. Fluorescence quenching and colorimetric properties of the chromogenic-dye probe were used as a detection strategy of H₂O₂. The enhanced catalytic property of nanoflakes of W/GCN was attributed to the unique structural characteristics, influenced by the dopant, that not only tuned its bandgap but also enhanced separation of electron–hole pairs as compared to planar and larger sized nanosheets of pristine GCN. This low-cost and rapid assay offered a very low limit of detection of 8 nM for the fluorescence quenching method and 20 nM for the colorimetric method. The linear range for fluorescence quenching and colorimetric H₂O₂ assays were from 10–500 nM and 35–400 nM, respectively. Therefore, this novel method of using W/GCN nanoflakes in fluorescence quenching and colorimetric based detections of H₂O₂ is expected to catch more interest on the topic of using non-enzymatic platforms for sensitive and selective detection of different analysts.

Representation of Tungsten doped graphitic carbon nitride for non-enzymatic-fluorescence quenching based detection of H₂O₂ with high sensitivity and accuracy triggered by the oxidation of RhB used as a fluorescence substrate.     

Colorimetric determination of ascorbic acid based on carbon quantum dots as peroxidase mimetic enzyme

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm. Interestingly, the ox-TMB could be further reduced by ascorbic acid (AA) leading to fading of the blue color and an absorbance decrease. Thus, a convenient and sensitive colorimetric method for detection of AA using CQDs as peroxidase mimics was established. Several factors, such as acidity, temperature, incubating time, and TMB concentration, which might influence the response of the analysis signal, were optimized. The results showed that the decrease of absorbance (ΔA) was in good linear agreement with AA concentration in the range of 1.0–105 μM, with a low detection limit of 0.14 μM. The feasibility of this method was also investigated in commercial beverages with the 94.3–110.0% recovery.

Carbon quantum dots (CQDs) were synthesized from litchi peel, exhibiting a peroxidase-like activity and enabling the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) in association with H₂O₂ to generate blue oxidized TMB (ox-TMB) with a strong absorption peak at 652 nm.     

Formation of functional nanobiocatalysts with a novel and encouraging immobilization approach and their versatile bioanalytical applications

The discovery of functional organic–inorganic hybrid nanoflowers (FNFs) consisting of proteins/enzymes as the organic components and Cu(ii) ion as the inorganic component has made an enormous impact on enzyme immobilization studies. The FNFs synthesized by an encouraging and novel approach not only showed high stabilities but also much enhanced catalytic activities as compared to free and conventionally immobilized enzymes. A recent development demonstrated that FNF formation has moved beyond the initial discovery in which enzymes and Cu²⁺ ions used as the organic and inorganic parts, respectively, are replaced with new organic (chitosan, amino acid and plant extracts) and inorganic (Cu²⁺ and Fe²⁺) materials. The new organic materials incorporated into FNFs act as Fenton-like agents and then show peroxidase-like activity owing to the metal ions and the porous structure of FNFs in the presence of hydrogen peroxide (H₂O₂). All FNFs have been widely utilized in many different scientific and industrial fields due to their greatly enhanced activities and stabilities. This review focuses primarily on the preparation, characterization, and bioanalytical applications of FNFs and explains the mechanisms of their formation and enhanced activities and stabilities.

The discovery of functional organic–inorganic hybrid nanoflowers (FNFs) consisting of proteins/enzymes as the organic components and Cu(ii) ion as the inorganic component has made an enormous impact on enzyme immobilization studies.     

Highly sensitive non-enzymatic hydrogen peroxide monitoring platform based on nanoporous gold via a modified solid-phase reaction method

In this work, nanoporous gold (NPG) fabricated using a modified solid-phase reaction method was developed as an electrocatalyst for the nonenzymatic detection of hydrogen peroxide (H₂O₂). The NPG morphology and structure were characterized by scanning electron microscopy and high-resolution transmission electron microscopy. The fabricated NPG exhibited a nanoporous framework with numerous structural defects. The NPG-based amperometric H₂O₂ sensor had a good selectivity, reproducibility, and low detection limit (0.3 μM) under near physiological conditions (pH = 7.4). The sensitivities of this sensor over concentration ranges of 0.002–5 mM and 5–37.5 mM were 159 and 64 μA mM⁻¹ cm⁻², respectively. These results indicate that the developed NPG is a promising material for the electrochemical sensing of H₂O₂.

Ge/Au/Ge triple-layered precursor was proposed to prepare nanoporous gold (NPG) with much smaller grain sizes and nanopores as an electrochemical sensor for highly sensitive and selective detection of hydrogen peroxide.     

Seed-mediated synthesis of Au@PtCu nanostars with rich twin defects as efficient and stable electrocatalysts for methanol oxidation reaction

Pt-based nanocrystals with a twinned structure are highly desirable to achieve high performances in both catalytic activity and durability for methanol oxidation reaction (MOR). However, it still remains great challenge for producing such twinned nanocrystals due to the high internal strain energy of Pt. Here we present a seed-mediated approach to generate Au@PtCu nanostars with a five-fold twinned structure using Au decahedra as seeds. The composition of Pt/Cu in the nanocrystals was tuned by varying the molar ratio of Pt to Cu salt precursors with the amount of Au seeds being the same. Through composition optimization, Au@Pt_1.2Cu nanostars achieved the highest specific (1.06 mA cm⁻²) and mass (0.18 mA mg_Pt⁻¹) activities for MOR, which were about 5.9 and 1.6 times higher than those of commercial Pt/C, respectively. After accelerated stability test (ADT) for 1500 cycles, such nanostars remained ∼95% of specific activity compared to a loss of ∼28% for commercial Pt/C, indicting their superior durability for MOR. We believed that this enhancement may arise from the unique twinned structure and possible synergetic effect between Pt and Cu components.

We present a seed-mediated approach to generate Au@PtCu nanostars with a five-fold twinned structure. The Au@PtCu nanostars exhibited better electrocatalytic properties in terms of activity and stability toward MOR relative to commercial Pt/C.     

Supported Pt–Cu bimetallic catalysts: preparation and synergic effects in their catalytic oxidative degradation of aniline

Catalytic Fenton oxidation is an effective way to remove organic pollutants in water, and the performance of the catalyst is a key issue for the competiveness of this method. In this work, various supported bimetallic Pt–Cu catalysts were prepared by different impregnation methods and their performances for catalytic Fenton oxidation of aniline in water were investigated. In the different impregnation methods employed, factors including the reduction method of the metal precursor, type of catalytic support, and loading of metal were investigated. The effect of different reduction methods on actual loadings of the active components on the supported Pt–Cu catalysts showed the order of (i) H₂ reduction > (ii) liquid phase methanal reduction. Meanwhile, compared with the monometallic catalysts, the Pt–Cu alloy phase (mainly in the form of PtCu₃) was generated and the specific surface area was significantly reduced for the bimetallic catalysts. In the process of Fenton catalytic oxidation of aniline, it was found that most of the prepared catalysts had a certain catalytic activity for H₂O₂ accompanied with aniline degradation. It was found that Pt_0.5Cu_1.5/AC (where AC denotes activated carbon) exhibited superb catalytic activity compared with all other prepared catalysts. In particular, aniline was almost completely mineralized in a neutral solution (500 mg L⁻¹ aniline, 0.098 mol L⁻¹ H₂O₂) after 60 min at 50 °C using Pt–Cu/AC (Pt: 0.5%, Cu: 1.5%). The characterization results showed that the Pt and Cu components were rather evenly distributed on the AC support for this catalyst. More importantly, there was an obvious synergic effect on the supported bimetallic catalyst between the Pt and Cu components for the catalytic oxidation of aniline.

An AC supported Pt–Cu catalyst prepared with a new methanal reduction method was found to be quite effective for catalytic Fenton oxidation of aniline in water. The Pt and Cu components showed a synergic effect for the catalytic process.     

Flower-like hydrogen titanate nanosheets: preparation,characterization and their photocatalytic hydrogen production performance in the presence of Pt cocatalyst

Flower-like hydrogen titanate nanosheets were prepared by a hydrothermal method and an assembling process. Then the Pt nanoparticles as cocatalysts were supported on the hydrogen titanate nanosheets through a photoreduction method. The samples were characterized by XRD, TG-DTA, ICP, SEM, TEM, XPS and UV-vis DRS. Their photocatalytic activity for H₂ production was also evaluated. The TEM results revealed that the as-prepared H₂Ti₂O₅·H₂O was with flower-like structure in which nanosheets were interlaced together. The formation mechanism of flower-like H₂Ti₂O₅·H₂O nanosheets was briefly proposed. With Pt cocatalyst, the flower-like H₂Ti₂O₅·H₂O had better photocatalytic activity (hydrogen production rate: 9.28 mmol g⁻¹ h⁻¹) and good cycling stability than original H₂Ti₂O₅·H₂O and commercial P25 under the same conditions. It was also found that the amount of cocatalyst Pt was positively correlated with photocatalytic performance.

Hydrogen titanate nanosheets were assembled into the flower-like hydrogen titanate nanosheets to obtain high photocatalytic performance.     

Copper-catalyzed synthesis of α-ketoamides using water and dioxygen as the oxygen source

The reaction employing H₂O and O₂ as the co-oxygen source in the catalytic synthesis of α-ketoamides is described. This copper-catalyzed reaction is carried out in a tandem manner constituted by the hydroamination of alkyne, hydration of vinyl–Cu complex and subsequent oxidation. Isotope labeling and radical capture experiments reveal that the oxygen atom of α-ketone at α-ketoamides derives from O₂ and the oxygen atom of amide group originates from H₂O.

The reaction employing H₂O and O₂ as the co-oxygen source in the catalytic synthesis of α-ketoamides is described. This Cu-catalyzed reaction is carried out in a tandem manner constituted by hydroamination of alkyne, hydration of vinyl–Cu complex and subsequent oxidation.     

Copper–tripeptides (cuzymes) with peroxidase-mimetic activity

Peroxidases are enzymes that use hydrogen peroxide to oxidize substrates such as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ATBS). In this study, we showed that copper–tripeptide complexes (“cuzymes”) also exhibited peroxidase-like activities. Different cuzymes could be formed by using various tripeptide ligands, such as GGG, GGH or HGG. However, the peroxidase-like activity of cuzymes depends on the sequence of the tripeptide (Cu–GGG > Cu–HGG > Cu–GGH). When ABTS was used as the substrate, the activity of Cu–GGG was 326 ± 1.5 U mg⁻¹ which was 2.5 times higher than that of horseradish peroxidase (HRP). Copper–tripeptide complexes were also used to degrade trypan blue dye. By using 0.2 mM Cu–GGG and 0.2% H₂O₂, 200 μM trypan blue could be degraded in 15 min at 50 °C. The degradation reaction followed second-order kinetics; the reaction rate was proportional to both H₂O₂ concentration and the copper–tripeptide concentration, but it was independent of the trypan blue concentration. Because copper–tripeptides catalyzed the oxidation reactions involving H₂O₂ effectively, they may have potential applications in biochemical assays and environmental remediation.

Copper–tripeptide complexs (cuzyme) exhibited peroxidase-like activities that use hydrogen peroxide to oxidize substrates such as 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ATBS) and trypan blue dye.     

Electrochemical detection of C-reactive protein using functionalized iridium nanoparticles/graphene oxide as a tag

C-reactive protein (CRP) has become a recognized indicator of inflammation. CRP concentration in serum is an important indicator for monitoring early heart damage, and it is also a newly discovered coronary heart disease-associated inflammatory factor. A conductive nano-hybrid material composed of Au NPs and ionic liquid functionalized molybdenum disulfide (Au NPs/IL-MoS₂) was prepared and utilized to immobilize primary CRP antibodies. Subsequently, 1,5-diaminonaphthalene (DN) was adsorbed onto graphene oxide (GO) through π–π stacking, which was used to load iridium nanoparticles (Ir NPs) as a tag to label secondary CRP antibodies. The large surface area of Au NPs/IL-MoS₂ and the excellent electrocatalytic properties of Ir NPs/GO-DN toward the reduction of H₂O₂ resulted in a highly sensitive assay for CRP antigens. This immunosensor exhibited wide linear ranges from 0.01 to 100 ng mL⁻¹ and a lower detection of limit of 3.3 pg mL⁻¹ (S/N = 3). This CRP immunosensor can be applied in real serum sample analysis with satisfactory results, indicating that the immunosensor has potential applications in biomedical detection.

Ir NPs@GO-DN was used as a tag to label CRP antibody to construct a sandwich CRP immunosensor.     

Boosting the hydrogen evolution reaction activity of Ru in alkaline and neutral media by accelerating water dissociation

Electrochemical water splitting via a cathodic hydrogen evolution reaction (HER) is an advanced technology for clean H₂ generation. Ru nanoparticle is a promising candidate for the state-of-the-art Pt catalyst; however, they still lack the competitiveness of Pt in alkaline and neutral media. Herein, a ternary HER electrocatalyst involving nano Ru and Cr₂O₃ as well as N-doped graphene (NG) that can work in alkaline and neutral media is proposed. Cr₂O₃ and NG feature strong binding energies for hydroxyl and hydrogen, respectively, which can accelerate the dissociation of water, whereas Ru has weak hydrogen binding energy to stimulate hydrogen coupling. The HER activity of Ru is greatly enhanced by the promoted water-dissociation effect of NG and Cr₂O₃. To achieve a current density of 10 mA cm⁻², the as-obtained Ru–Cr₂O₃/NG only needs a very low overpotential of 47 mV, which outperforms the activity of Pt/C in alkaline media. The strategy proposed here, multi-site acceleration of water dissociation, provides new guidance on the design of a highly efficient, inexpensive, and biocompatible HER catalyst in nonacidic condition.

The electrocatalytic activity of Ru in non-acidic media for hydrogen evolution reaction can be greatly boosted by Cr₂O₃ and N-doped graphene.